1. Technical Field
The present invention relates generally to a method for making snack food products. More particularly, the invention relates to a method of utilizing extrudate stretching for making an expanded, shaped, pellet snack with annular cavities.
2. Description of Related Art
Pellet, or xe2x80x9chalf productxe2x80x9d technology, is known in the snack industry for producing puffed snack products. Pellet products, prior to puffing (expansion), provide several advantages, which include the following: a high bulk density, which makes them less expensive to ship, breakage resistance during shipment, and the ability to form intricate shapes. Once puffed pellet products have a light, expanded texture because of their low product density and a thin product wall thickness, for example less than 0.20 inches.
Generally, an expandable pellet is one that increases in volume by upwards of 100% from the rapid vaporization of water within the pellet during rapid heating of the pellet. Consequently, the density of the pellet decreases. For example, the initial density of a typical pellet piece is greater than about 40 lb/ft3 and following expansion is reduced down to a final density of less than about 25 lb/ft3.
Typical pellets require processing to produce a finished snack product. In a first step, the ingredients, which generally include cereal products and starches, are hydrated to form an extrudable mixture for forming pellets. The extrudable mixture is subsequently gelatinized to create dough that is subsequently passed through a die where after the extruded mixture is cut into pellets. After formation, the unfinished pellets, which contain from about 20% to about 30% moisture by weight, are processed through a dryer to arrive at a final moisture of about 9% to about 18% for either storage or later processing after moisture equilibration.
To produce a product that has desirable texture, density and other characteristics, the pellets made using the prior art method need to be dried and moisture equilibrated, which is essentially a curing stage. This curing stage can extend from a period of less than an hour up to several days or longer. This step reduces the moisture content significantly from about 25% down to about 12% for example. Once dried, the pellets can then be expanded by heating with, for example, frying, baking (hot air impingement), or microwave heating. This drying/curing stage adds expense and time to the pellet manufacturing process.
Processes for producing pellets for use as a snack food product are known in the art. For example, U.S. Pat. No. 3,348,950 to Weiss describes a process for making snack food product by first mixing together corn, sucrose, water, and flavoring. This mixture is combined with a second mixture of yellow corn grits, water, and sodium bicarbonate. The combined mixture is pre-cooked under pressure of 14 psi to 20 psi and temperatures between 247xc2x0 F. and 259xc2x0 F. The gelatinized dough is shaped, and then dried and/or moisture equilibrated before puffing using deep-fat frying. This process requires extensive drying time and a tempering period of xc2xd to 2 hours.
In pellet processing, it is possible to use dies with intricate designs. Because of the high viscosity or xe2x80x9cstiffnessxe2x80x9d of the dough, it is possible to cut the dough as it exits the die face and retain the intricate die design in the cut, unexpanded pellet. Many food products exist which are extruded through a ring-shaped die to create an annular cavity, with perhaps the most common being macaroni. Macaroni, however, requires extensive drying time and is not usually expanded as a snack product. Macaroni is also not commonly injected at the die with a gas or fluid. While filled tubular snack products are known, they are not expanded pellet products, U.S. Pat. No. 3,615,675 to Fowler et al. discloses an apparatus to fill an extruded, tubular snack with a suitable material. The disclosed procedure expands the product at the die and does not produce a pellet product. The product is also not stretched. U.S. Pat. No. 4,259,051 to Shatila discloses an apparatus and method for extruding one material to surround another. However, no disclosure is made of using the apparatus to make pellet snacks, and furthermore, there is no discussion of stretching the product.
Animal protein is known to be used for forming pellets. U.S. Pat. No. 4,163,804 to Meyer et al. describes producing expandable pellets by extruding animal parts at temperatures between 250xc2x0 F. and 330xc2x0 F. with an extrusion pressure over 500 psig. It is essential to this process that the raw material be animal parts that have a high average undenatured protein (collagen) content. The high collagen content allows the formation, under the disclosed process conditions to be formed after extrusion into a shaped sustaining form and cut into puffable pellets. It is disclosed that stretching ratios of from 2:1 to 5:1 are used in some applications of this invention but stretching is not used when annular shapes are made. No disclosure is made of stretching an annular shape and no gas or fluid is injected in the cavity of the annular shapes.
U.S. Pat. No. 5,645,872 to Funahashi describes an apparatus for processing food in a tubular shape and filling it with a hot liquid. This is done to prevent collapsing of the product wall because of the flowability of the product material. No disclosure is made of using this apparatus to make pellets and no method of stretching the product is disclosed.
U.S. Pat. No. 5,750,170 to Daouse et al. discloses a method of co-extruding food material in a tube shape with filling. The dough tube and filling are supported on a movable support and then cut with blades while being transported. The blades cause slight stretching of the tube only at the point of cutting but there is little or no manipulation or stretching of the remainder of the dough. No disclosure is made of using this apparatus to make a pellet product.
U.S. Pat. No. 6,242,034 to Bhaskar et al. describes a process to make tube-shaped pellets. The process involves using tension rolls to stretch a ribbon extruded from the die face. This stretching is at less than a 2:1 ratio, and these pellets still require a drying step prior to expansion. There is also no air or fluid injection into the product because an annular die is not used.
U.S. Pat. No. 6,328,550 to Sheen et al. discloses a multiple extrusion nozzle for extruding a tube-shaped casing with filling injected inside the casing. However, no disclosure is made of using the apparatus to make a pellet product nor is there disclosure of stretching the product.
A process to produce an expanded, shaped, pellet snack product with annular cavities and a low bulk density similar in texture to a pellet product while avoiding the processing detriments for a pellet process is desired. Further, it would be advantageous to produce a shaped snack product with annular cavities without the need for a pellet finish drying and/or conditioning stage. Consequently, a need exists for producing a shaped pellet snack product with annular cavities that is easily produced while having a desirable texture and shape.
The present invention is an improved method for producing a shaped pellet product with annular cavities having a light texture once expanded, without the need for a dehydration/tempering step of over 10 minutes prior to expansion. A farinaceous meal, which can include yellow corn meal, white corn meal, corn masa flour, rice meal, wheat flour, or mixtures thereof is provided to an extruder along with a source of water. In addition to the farinaceous meal, a protein such as soy protein can be substituted, at least in part, for some of the meal. Other ingredients can be used in addition to the aforementioned such as sugar, dextrose, dry molasses, wheat bran, emulsifier, shortening, modified food starches, leavening, and others.
During extrusion, the mixture is mechanically sheared and gelatinized within the extruder under conditions of shear, pressure, and temperature for opening the starch granules. The mixture is extruded through a die insert that forms an extrudate with an annular cavity. Upon passing through the die, the extrudate forms a tube, which xe2x80x9cprepuffsxe2x80x9d upon exiting the extruder due to steam being released from the reduction in pressure. This prepuffing facilitates a reduction in the moisture content of the ribbon from about 15% to about 30% down to about 9% to about 20%.
To convert the prepuffed tube to an unpuffed pellet consistency, the tube is stretched by passing it through a series of rollers. To facilitate this, the tube has air, other inert gas, or liquid injected into the cavity in the middle thereof. This injection provides a positive pressure within the tube of extrudate to allow it to be gripped by rollers without collapsing the extrudate tube.
The extrudate with an annular cavity is then passed between the stretching rollers whereby the linear velocity of the extrudate is increased by at least 1.5 times, more preferably at least three times. The tension in the ribbon, provided by the stretching rollers, counteracts the expansion caused by the prepuffing at the die due to steam formation. This results in the ribbon, after initial expansion, to return to an unexpanded, thin pellet-like nature with a density greater than 40 lb/ft3 and a thickness of less than 0.1 inches. The stretched extrudate is then cut into shaped pellets with annular cavities that are subsequently puffed in a hot air puffer for example. Advantageously, the stretched pellets do not require any drying or conditioning such as moisture equilibration prior to being puffed. Thereafter, the puffed pieces are then finish dried and seasoned prior to packaging.
Regarding the shapes produced, the shaped product can resemble, for example, a ring or a wheel with one or more spokes. Depending on the die insert used, one or more lines of extrudate can be allowed to bisect the wheel. Each annular cavity of the extrudate is supplied with air or other gas to allow sufficient pressure to retain the ring or wheel shape during the stretching phase. Once stretched, the extrudate is cut into pellets for additional processing into puffed snack products. Depending on the speed of the cutter, thin shapes such as rings, or longer shapes, such as tubes, can be made. Also, one or both ends of the cut pieces can be sealed forming them into pocket or pillow shaped pieces.
After puffing, shaped snack products with annular cavities are produced having a low bulk density similar to conventional pellet type products. However, this is advantageously achieved without the need for a drying and/or conditioning step prior to puffing.
The above as well as additional features and advantages of the present invention will become apparent in the following written detailed description.